In the operation and maintenance of power plants, such as, internal combustion engines, the products of combustion contain a number of pollutants or noxious components in the exhaust gas or fumes. It is generally recognized that the more complete or efficient the combustion of fuel, the greater the reduction in the pollutants present in the exhaust and greater overall economy and performance of the engine. Thus, while catalytic converters have been employed in the exhaust system which are effective in reducing pollutant levels to some extent, they do not improve the economy or performance of the engine and do not satisfactorily reduce all pollutants present in the exhaust.
It has been proposed in the past to employ pollutant sensors in the exhaust of a motor vehicle to regulate the fuel/air ratio or mixture. Typically, however, such sensors are utilized to regulate the fuel in order to make the mixture either richer or leaner. Although this will contribute to some degree to maintain the combustion gases closer to the stoichiometric condition, it is not nearly as effective as regulating the delivery of a supplementary source of oxygen under pressure into the fuel/air mixture. The use of pure oxygen thereby avoids the introduction of additional nitrogen, for example, by increasing the ratio of oxygen to nitrogen in the air from 21% oxygen to 79% nitrogen to 23% oxygen to 77% nitrogen and has been found to be vastly more effective in maintaining the desired stoichiometric condition.
Other systems have been devised for reducing the pollutant level and achieving more complete combustion either by regulating the fuel/air mixture and/or by recirculating the products of combustion from the exhaust back through the carburetion system. For example, U.S. Letters Pat. No. 3,851,632 to Teshirogi is directed to a method and apparatus for controlling the pollutant level in the exhaust fumes of a diesel engine by recirculating the fumes and adding oxygen to the recirculated fumes when the oxygen level in the exhaust gases falls below a predetermined amount. Specifically, Teshirogi determines a particular level of oxygen to be maintained in the recirculation of the exhaust and injects oxygen as a function of the pollutants present in the exhaust. However, the system necessarily requires that engine power be utilized to recirculate the exhaust gases for more complete burning and ultimate reduction in the pollutant level. Other approaches have been taken to increase engine performance by regulating the amount of fuel in the fuel/air ratio as typified by U.S. Letters Pat. No. 3,738,341 to Loos and No. 3,745,768 to Zechnall et al. However, no attempt has been made to control the oxygen content in the air intake and to do so in direct response to the pollutant level in the exhaust. In this relation it is highly desirable to be able to accurately and closely control the amount of oxygen delivered in direct response to the pollutant level in the exhaust.
U.S. Letters Pat. No. 3,556,066 to Muirhead combines oxygen with a supplementary fuel to introduce into the fuel/air mixture but not in response to a particular pollutant level and is concerned more with the metering of the amount of fuel in relation to the amount of supplemental oxygen supplied to the carburetor. In this regard it is important to establish the optimum stoichiometric condition of the power plant or engine and to regulate the amount of oxygen furnished to the carburetion system necessary to maintain the stoichiometric condition.